1. Field of the Invention
The present invention concerns a target for cathode discharging arc ion plating used when the surface of a substrate such as a cutting tool or jig is covered with a hard film.
2. Description of the Related Art
The cathode discharging arc ion plating is a method of discharging an electron stream of a large capacity (several tens to several hundreds A) from the surface of a target constituting a cathode to an anode in vacuum during arc discharge, evaporating and ionizing the target by a Joule heating when electrons are emitted from the cathode, thereby conducting deposition on the surface of a substrate such as a cutting tool. An AlTi system target is mainly used as a target for cathode discharging arc ion plating for forming a hard film, for example, with nitrides or carbonitrides. A target comprising Al and Cr as an essential ingredient is sometimes also used for the formation of a hard film since the oxidation resistance is improved by using Cr instead of Ti in the AlTi system targets.
Upon arc discharging, arc spots (cathode spots) as electron emission points are formed on the surface of a target. A desired state of the arc spot is that one or plural arc spots are present during discharge and move at a high speed (several to several tens m/sec) and uniformly on the target. When movement of arc spots stagnate, melted portions referred to molten pool are formed near the stagnation portions. Then, the molten portions are scattered by the pressure increase along with explosive solid-gas phase conversion and deposited on the surface of the substrate. The deposited molten liquid droplets are referred to as macro particles which roughen the surface of the formed film and deteriorate the performance of the film.
In a case where the target is homogeneous comprising a single metal or single tissue, since spots tend to move uniformly on the surface of the target, problems less occur. On the other hand, when the target is inhomogeneous, that is, the composition comprises plural ingredient, or the tissue comprises plural phases, the spots less tend to move uniformly to result in a problem that macro particles are liable to be caused to the film.
As has been described above, while the use of a target comprising Al and Cr as an essential ingredient has been attempted as a target for cathode discharging arc ion plating, it is difficult to form a film of high quality and it has not yet reached a practical level at present. This is because the target comprises plural ingredients. In addition, since Cr tends to react more with Al compared with Ti or the like, Al—Cr compounds are formed easily in the course of target production. The Al—Cr compounds cause not uniform movement of spots which form macro particles.
As a relevant technique, Japanese Patent Laid-Open Hei 10-60636 describes a sputtering target comprising Al as a main ingredient and containing compound forming elements such as Ti and Zr. However, the patent publication does not specifically disclose a target contained Al and Cr as the essential ingredient. Further, in the patent publication, it is described that it may suffice to remain the element forming a compound with Al in the state of a metal or element in the target. Cr tends to react more easily with Al and form compounds, compared with Ti or the like. Particularly, in discharging arc ion plating, formation of the compounds per se gives an undesired effect on the arc discharging, while in sputtering it does not give such an effect. Accordingly, the technique of the patent publication above can bot prevent abnormal discharging or splash upon sputtering which is caused during fabrication by cracking of inter-metallic compound which is formed by reaction of Al and a compound forming elements in the matrix upon sintering.